Method and apparatus for accurately dispensing liquids and solids

ABSTRACT

A system for metering and dispensing single and plural component liquids and solids as described herein. The dispensing system has a microprocessor-based control system and volumetrically efficient non-reciprocating pumps which provide a very accurate control of component ratios, shot sizes, flow rates and dispense durations. The dispensing system maintains constant pressure between the output of the pump and the dispense head. The progressive cavity pump is formed from individual, interlocking pressure sections, each of which has a double helix bore. A dispense head for a plural pump dispensing system using sealed bellows with rods extending therethrough associated with an actuator. The sealed bellows attach at one end to the body of the dispense head and at the other to the rods. The rods extend into a chamber and have a sealing end selectively engaging the exits from the chamber. The dispense head may further incorporate an actuator controlling the rods, a controller controlling the pumps and the actuator to close down the system simultaneously and the pumps themselves. A static mixer may be used with the exits. The system also has numerous feedback components for accurately controlling the pressure, flow rates, fluid levels and amounts of fluids dispensed.

This application is a divisional application of U.S. patent applicationSer. No. 08/752,768, filed Nov. 20, 1996, issuing as U.S. Pat. No.5,857,589 on Jan. 12, 1999, the disclosure of which is incorporatedherein by reference.

TECHNICAL FIELD

The field of the present invention is devices that meter and dispensesingular and plural component liquids and solids.

BACKGROUND OF THE INVENTION

Systems for mixing and dispensing singular and multicomponent materialsare well known in the art. Such systems typically include pumpingmechanisms for pumping and metering separate materials, such as a basematerial and an accelerator material, in a prescribed ratio to a mixingdevice that thoroughly mixes these materials together. The mixedcomposition then flows out of a dispensing nozzle directly to thesurface or point of application where the composition is desired.

When a curable composition is desired, two or more suitable materialsare mixed to interact with each other to create a flowable, curablecomposition which will set or harden to a non-flowable state. The timerequired for a curable composition to harden is referred to as the"cure" time and often is a short period of time. Such resulting curablecompositions have been used, for instance, as adhesives, sealants andpotting materials in a wide variety of industrial applications.

Production environments can impose limitations on how a dispensingdevice should operate. For example, in a production environment, it isdesirable for the curable composition to cure as rapidly as possible sothat subsequent production operations can be performed on the productionitem without having to wait a significant time for curing to occur.

Further, production requirements often include the need to dispense aprecise amount of a properly constituted composition. A deviation in theactual ratio of the constituent materials dispensed may alter thestrength, viscosity and/or other properties and attributes of thecomposition. Thus, a dispensing system should dispense the desired ratioand quantity of constituent materials as accurately as possible. In manycases, the desired ratio is expressed as a function of the weight ormass of two constituent components. Nonetheless, the two constituentcomponents are generally supplied to the mixer by volumetric meteringpumps which control the volumetric ratio of the two components, ratherthan their weights or masses. The volumetric ratio fails to account forany changes in density and changes in mass that may occur when thecomponents are subjected to temperature or pressure change.

Also, production items often move along a production line at a setspeed. Therefore, the flow rate of the dispensed composition should bekept or maintained as constant as possible so that the time required todispense the proper amount of composition onto or into the productionitem remains constant.

An assembly line operation may further require that the composition bedispensed intermittently because the composition is applied toproduction items that are separated spatially and temporally. Dispensingcompositions intermittently may cause a loss of flow control and/orratio control. During the first few seconds of dispensing a composition,a transient imbalance phenomenon may arise from the elasticity ofmaterials in the dispensing system and/or changing pressures caused bycycling the dispenser. When pressure changes, the volume of storedmaterial between the mixer and the pump changes. In other words, changesin pressure may introduce an error into the weight or mass ratio of theconstituent components because a higher pressure results in a componenttaking less volume than the component would otherwise take, or in anexpansion or shrinkage of the hoses, fittings and tubes. The loss ofcontrol may result in inaccurately dispensed quantities or ratio ofmaterials. This loss of flow control can occur separately or in additionto the loss of ratio control. A loss of ratio control occurs when thetransient imbalance phenomenon causes the dispensing system to dispensetoo much or too little of one constituent material, thereby resulting inan improperly constituted end product. In other words, even if the ratiocontrol is not lost during the first few seconds of dispensing acomposition, the flow control may be lost. Therefore, it is desirous tocontrol both the ratio of constituent materials and the flow rate ofdispensing of the resulting composition.

Dispensing machines may be used to create various types of compositions.A dispensing machine may be required to dispense two or more constituentmaterials to form a first composition and then switch to dispense eitherthe same constituent materials in a different ratio or other constituentmaterials to form a second composition. Thus, it is desirable for adispensing machine to change what materials are dispensed, thequantities of materials dispensed and/or the ratio of constituentmaterials while maintaining the device's ability to control accuratelythe quantity, ratio, flow rate and other dispensing criteria. Currentdispensing systems fail to satisfy these needs and require users to shutdown the dispensing machine and go through a lengthy calibration cyclein order to adjust the machine to the viscosity and/or other propertiesof the constituent materials.

Some dispensing systems include vats capable of holding large amounts ofa constituent material. Motor-driven agitators are placed inside the vatto maintain the material homogeneity. As the amount of material held ina vat is consumed, the agitator requires either less velocity or lesscurrent to mix the remaining material. However, in present dispensingsystems, as the remaining material in a vat decreases, an agitatorcontrolled by conventional means may over-agitate the material,resulting in frothing or the introduction of air bubbles. This frothingof the material could adversely affect the accuracy of the amount ofmaterial dispensed.

These concerns and problems may be further exacerbated when a dispensingsystem attempts to dispense a composition formed by mixing a solidpowder with a liquid. Additional issues such as maintaining properratios and homogeneity arise.

Ideally, a dispensing system should be able to accurately control theratio of each constituent material dispensed, the flow rate of eachconstituent material dispensed, the flow rate of the resultingcomposition, and the amount of the constituent materials and theresulting composition dispensed and be able to maintain such accuracyover time and various operating conditions. However, present dispensingsystems fail to satisfy these attributes.

SUMMARY OF THE INVENTION

An aspect of the present invention is a dispense head for a plural pumpdispensing system using sealed bellows with rods extending therethroughassociated with an actuator. The sealed bellows attach at one end to thebody of the dispense head and at the other to the rods. The rods extendinto a chamber and have a sealing end selectively engaging the exitsfrom the chamber. The dispense head may further incorporate an actuatorcontrolling the rods, a controller controlling the pumps and theactuator to close down the system simultaneously and the pumpsthemselves. A static mixer may be used with the exits.

A ninth, separate aspect of the present invention is a device fordispensing single and plural component liquids and/or solids where thedevice includes feedback components so that the device can accuratelyadjust and control the pressure, flow rate, quantity and volume offluids dispensed.

A tenth, separate aspect of the present invention is a device fordispensing single and plural component liquids and/or solids where thedevice includes agitators and feedback components that allow the deviceto determine the level of the material remaining in the vats and whichcontrols agitation speed to prevent frothing and aeration of thematerial.

An eleventh, separate aspect of the present invention is a dispensingdevice for dispensing plural component liquids and powders whereby apowder is dispensed and combined with a single or plural componentliquid.

A twelfth, separate aspect of the present invention is a machine whichis capable of changing ratios of delivered components under softwarecontrol, both from shot-to-shot and during the time the material isbeing dispensed.

A thirteenth, separate aspect of the present invention is a machinewhich is capable of changing delivered material composition undersoftware control to adjust material pre-cure and part curecharacteristics, such as viscosity, color and thixotropic factors.

A fourteenth, separate aspect of the present invention is a dispensesystem that can repeatedly dispense production quantities into parts atan accurate rate and volume.

A fifteenth, separate aspect of the present invention is a dispensesystem that checks the pump and plumbing for leaks and trapped air toinsure optimum performance of the dispense.

BRIEF DESCRIPTION OF THE DRAWINGS

The various objects, features and advantages to the present inventionwill be better understood by considering the Detailed Description of aPreferred Embodiment which follows together with the drawings, wherein:

FIG. 1 is a block diagram of a preferred embodiment of a dispensingsystem which dispenses a single or plural component fluid.

FIG. 2 is a cross-sectional diagram of a dispense head in the openedposition.

FIG. 3 is a cross-sectional diagram of a dispense head in the closedposition.

FIG. 4 is an exploded cross-sectional view of the bellows assembly.

FIG. 5 is a partially exploded cross-sectional view of the bellowsassembly.

FIG. 6 is a cross-sectional view of the bellows assembly as mounted tothe valve rod and rod end.

FIG. 7 is a cross-sectional view of the bellows.

FIG. 8 is a cross-sectional diagram of a preferred embodiment of thepump stator assembly.

FIG. 9 is a side view of a pressure section of the pump stator assemblyof FIG. 8.

FIG. 10 is a perspective end view of a pressure section of FIG. 9.

FIG. 11 is an end view of a pressure section of FIG. 10.

FIG. 12 is another side view of a pressure section of FIG. 9.

FIG. 13 is a cross-sectional view of the pump stator assembly of FIG. 8and illustrates the flow pattern of fluids passing through the pumpstator assembly.

FIG. 14 is a cutaway view of a partial pump stator assembly having asingle helix rotor within the double helix bore.

FIG. 15 is a cross-sectional view of a partial pump stator assembly androtor.

FIG. 16 is a diagram showing the position of the single helix rotor asthe rotor rotates within the double helix bore of a pump statorassembly.

FIG. 17 is an electrical block diagram of a preferred embodiment of amotor controller.

FIG. 18 is a block diagram of a preferred embodiment of a dispensingsystem which dispenses a powder and a single or plural component fluid.

FIG. 19 is a diagram showing how FIGS. 20-23 connect to create asoftware flowchart for controlling aspects of the dispensing system.

FIGS. 20-23 are software flowcharts for controlling aspects of thedispensing system.

FIG. 24 is a software flowchart that describes the RS232 and DIP switchsoftware for the motor controller.

FIG. 25 is a software flowchart that describes the RS232 data flow inthe motor controller.

FIG. 26 is a software flowchart that describes the motor controllertimer interrupt software.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates a block diagram of a dispensing system 1 whichdispenses a single or plural component fluid. In FIG. 1, the dispensingsystem 1 has a plurality of vats 2, 4, each of which holds a fluid 6, 8that is a constituent material of the desired final product. Agitators9, 10 stir the fluids 6, 8 in order to maintain the fluids ashomogeneously as possible. The dispensing system 1 has a master controlunit 14 which may be a CPU, microprocessor, microcontroller, arithmeticlogic unit, ASIC, field programmable gate array, or other logic controlcircuit. The master control unit 14 receives data and commands via datainterconnects 16, 18 from a user input device 20 and/or a programminginput device 22. The user input device 20 may be a keypad, buttons,switches, barcode reader, or other input device. Depending on the input,the master control unit 14 controls various aspects of the dispensingsystem 1. For example, the master control unit 14 has lines 26, 28 fortransmitting commands and receiving data from pump controllers 30, 32which in turn direct and manage pumps 34, 36. The control unit 14calculates desired pump parameters, such as acceleration, speed andduration, based on data entered through aforementioned user inputdevices and from data resident in the software and hardware of thecontrol unit. Primary items of information stored in the residentsoftware are the dispense volume of each pump rotation, and the ratiobetween motor rotation and pump rotation. The software then calculatesthe number of motor rotations to deliver the desired quantity ofmaterial, including velocity or rotational speed. If one revolution ofthe pump outputs a known volume of a fluid, the pump constant, thecontrol unit 14 calculates the tick count to control the number ofrevolutions and partial revolutions the pump makes and thus, direct thequantity of the fluid to be dispensed. The desired pump parameters arethen downloaded to the pump controllers 30, 32, via the data lines 26,28 and stored. A signal to begin a cycle is sent simultaneously to eachpump controller 30,32 by the control unit 14, both pumps 34, 36 activateunder their respective programs. The motor controllers 30, 32 then countthe ticks received from absolute position encoders 38, 40 over time tomanage the rotational speed or acceleration of the pumps 34, 36. Theabsolute position encoders 38, 40 are coupled mechanically to the shaftsof the motors 39, 41 and may operate optically, mechanically,electrically or magnetically. The encoders 38, 40 count tick marks todetect the position of the shafts as they rotate. The encoders 38, 40send pulses (i.e., a number of ticks over time) representing the shaftposition information to the motor controllers 30, 32. As later describedin FIG. 17, the pulses enter a control circuit 190 (within the motorcontrollers) and are used by the control circuit 190 to control powerdrivers 200 and the motors 39, 41. Thus, the pulses from the encodersare used by the motor controllers to adjust or fine tune the operationof the motors 39, 41. The motor controllers 30, 32 may send status andother information including encoder information to the master controlunit 14. Thus, the motors 39, 41 and in turn the pumps 34, 36 arecontrolled by a pump control system including the master control unit14, the motor controllers 30, 32 and the encoders 38 and 40.

If a revolution of the pump outputs a known volume of a fluid, the pumpcontrol system, either the master control unit 14 or the motorcontroller depending on which device is to have feedback control in aparticular design, can use the encoder tick measurement of the number ofrevolutions and partial revolutions made by the pump and thus, calculatethe expected volume of the fluid dispensed. The master control unit 14may count the ticks from the encoders 38, 40 over time to determine therotational speed or acceleration of the pumps 34, 36. Thus, the pumpcontrol system including the encoders 38, 40 measure pump displacementand rate to act as pump movement sensors.

The action of the pumps 34, 36 draws fluids 6, 8 into the pumps throughvat fluid lines 42, 44. The fluids 6, 8 pass into the pump fluid lines46, 48 and into a dispense head 49 having a separate chamber 51 for eachpump fluid line 46, 48. From the dispense head 49, the fluids pass intoa static mixer tube 50. The static mixer tube 50 has internalprojections that mix the fluids 6, 8 together and dispense an endproduct 52 through the output nozzle 53 of the static mixer tube 50. Theend product 52 may be dispensed onto a scale 54 which weighs the endproduct. The dispensing system 1 receives DC power from a DC powersupply 56.

Thus, the dispensing system as shown in FIG. 1 is a two-channel system,where each channel handles the dispensing of one fluid. The firstchannel (channel A) includes the vat 2, vat fluid line 42, pump 34, pumpcontroller 30, encoder 38, pump fluid line 46 and dispense head 49. Thesecond channel (channel B) comprises the vat 4, vat fluid line 44, pump36, pump controller 32, encoder 40, pump fluid line 48 and dispense head49. The dispensing system may also be modified to include additionalchannels and include additional vats, agitators, pumps, fluid lines andother components as desired to dispense three or more componentmixtures.

Pressure transducers 58, 60 send feedback information about the pressurein the pump fluid lines 46, 48 to the master control unit 14 so that themaster control unit 14 can monitor the pressure in the pump fluid lines46, 48 from the output of the pumps 34, 36 to the dispense head 49. Theability to maintain a constant pressure from the output of each pump 34,36 to the dispense head 49 helps assure that the fluid is compresseduniformly and constantly so that an accurate amount of fluid isdispensed. Additionally, if there is a blockage or malfunction, thepressure transducer will signal a preset overpressure situation, and thesystem will shut down. Similarly, flow meters 66, 68 measure the flowrates within the pump fluid lines 46, 48 and transmit flow rateinformation to the master control unit 14, thereby allowing the mastercontrol unit 14 to monitor the fluid flow rates. Should the flow ratesdiffer from calibration data, the system can be shut down and an errorreported.

The dispense system can also use information from the pump controllers30, 32 and the flow meters 66, 68 and other feedback sensors to checkthe pump and plumbing for leaks and trapped air. Appropriate errormessages may be issued to the user to insure optimum performance. Thedispense system may change the delivered material composition, fromshot-to-shot or during the time the material is being dispensed, inorder, for example, to adjust material pre-cure and post curecharacteristics such as the viscosity, color and thixotropic factors ofthe material.

The dispense head 49 has positive cutoff valves 70 which aresymbolically shown in FIG. 1. The positive cutoff valves 70 arecontrolled by the master control unit 14 and serve to cut off the flowof fluids in the dispense head 49 whenever appropriate (i.e., when thedispense cycle is completed). The control lines between the mastercontrol unit 14 and the positive cutoff valves 70 are not shown in FIG.1.

Agitators 9, 10 in the vats 2, 4 are driven by agitator motors 11, 12.The agitators 9, 10 are illustrated as stir paddles but may be any typeof agitator well known in the art. The agitators 9, 10 run at a constantdesired speed. However, as the level of the fluid in a vat 2, 4 falls,less current is required to drive the agitator at the same speed. Themaster control unit 14 can detect the reduced current flow and determinethe amount of fluid remaining in the vat. Alternately, the system can bemade to maintain a constant current instead of constant motor speed. Anadditional encoder and motor controller similar to those previouslydescribed are coupled to each agitator motor so that the motorcontroller (and master control unit 14) can receive rotational positioninformation from the agitator motors. Accordingly, the master controlunit 14 can determine the rotational speed of each agitator to determinethe level of fluid remaining in the vat. As the fluid level in the vatfalls and as the current flow to the agitator motor is kept constant,the rotational speed of the agitator motor increases. The master controlunit 14 can measure the rotational speed of the agitator motor todetermine the level of fluid remaining in the vat. The master controlunit 14 can also decrease the current to the agitator motor when themaster control unit 14 detects that the motor speed has increased. Eachvat 2, 4 has a float connected to a normally closed switch. When thefluid level falls below a certain level, the float falls and triggersthe switch to open.

The dispensing system of FIG. 1 operates as follows:

1. The user calibrates the dispensing system (as described later) andthe dispensing system calculates how much the pump motors must rotate inorder to dispense a unit weight of a fluid or mixture.

2. The user enters program mode to set up shot parameters.

3. In response, the master control unit 14 queries the user for variousparameters of the dispense cycle.

4. The user inputs the desired ratio of component fluids, the shot sizeof the end product, and either the flow rate or the time duration of thedispense cycle.

5. The master control unit 14 determines the proper pump parameters inorder to feed constituent materials at the desired rate and downloadsinstructions to the pump controllers 30, 32.

6. The user initiates a dispense cycle by depressing a foot pedal,button or switch. The system can also be initiated by a signal from apressure transducer to dispense more fluid.

7. The master control unit 14 starts the dispense cycle by opening thepositive cutoff valves 70 in the dispense head 49 and by starting thepumps 34, 36.

8. The pump controllers 30, 32, flow meters 66, 68 and pressuretransducers 58, 60 feed back information about the rotational speed ofthe pumps, flow rates and pressures to the master control unit 14. Thepump controllers 30, 32 self monitor for accuracy and feed errors backto the master control unit 14. The master control unit 14 uses thisinformation to monitor the pump for correct rotational speed, flow ratesand pressures.

9. The pressure transducers 58, 60 check for blockages in the pump fluidlines 46, 48 and shut down the dispensing system to prevent damage tothe system if the detected pressure exceeds a pressure limit set point(i.e., an overpressure condition).

10. The pumps 34, 36 and the positive cutoff valves 70 maintain theproper pressure in pump fluid lines 46, 48 by functioning as positivecutoffs between shot cycles. When the dispense cycle ends, the mastercontrol unit 14 closes the positive cutoff valves 70 and stops pumps 34,36.

11. The master control unit 14 analyzes received information anddetermines whether a dispense cycle was successfully completed.

12. Should there be a need to modify the pump function to insure correctdispense characteristics, the master control unit 14 sends new commandsto the pump controllers 30, 32.

13. Steps 6-12 are repeated as needed for different quantities, ratiosand durations.

FIG. 2 is a cross-sectional diagram of a dispense head 49. The dispensehead 49 is a combination manifold/on-off valve that controls the flow offluids. The dispense head 49 includes a bellows assembly 80. FIG. 4illustrates an exploded crosssectional view of the bellows assembly 80and FIG. 5 depicts a cross-sectional view of a partially constructedbellows assembly 80. The bellows assembly 80 includes a bellows 82. Thebellows 82 is a compressible corrigated metal alloy sleeve that is shownin greater detail in FIG. 7. As shown in FIG. 7, the bellows 82 has twoends 84, 86. Returning to FIGS. 4 and 5, a valve rod 88 is inserted intoa center hole of the bellows 82. The bellows 82 slides freely along thelength of the valve rod 88. The valve rod 88 is also inserted into anaperture of a rod seal ring 90. The rod seal ring 90 is not affixed tothe valve rod 88 and is also free to slide back and-forth along thelength of the valve rod 88.

FIG. 6 is a cross-sectional view of the bellows assembly 80 and showshow the bellows assembly 80 is affixed to the valve rod 88 and the rodseal ring 90. One end 84 of the bellows 82 is hermetically sealed to theraised lip 92 of the valve rod 88 by welding, soldering, brazening orother means. The other end 86 of the bellows 82 is similarlyhermetically sealed by welding, soldering, brazening or other means tothe rod seal ring 90. Thus, as the valve rod 88 extends and retractsfrom the rod seal ring 90, the valve rod 88 alternately compresses andexpands the bellows 82.

A seat/rod seal 94 slides over and around an end of the valve rod 88 andabuts the raised lip 92 of the valve rod 88. A retaining screw 96 entersthe opening of the seat/rod seal 94 and screws into mating threads 98 ofthe valve rod 88. The retaining screw 96 holds the seat/rod seal 94 inplace.

Returning to FIG. 2, each bellows assembly 80 is shown as mounted in aseparate chamber 51 within the dispense head 49. The dispense head 49has two inlets 100. The inlets 100 receive fluids 6, 8 from the pumpfluid lines 46, 48, and go perpendicularly into the illustration of FIG.2. A pneumatic valve actuator includes air cylinder 101 having a piston102 which moves freely within the air cylinder 101. Screws 103 passthrough passages in the free piston 102 and engage the mating screwthreads 99 of the valve rods 88 to attach the valve rods 88 to the aircylinder 101. Each air chamber 104 of the air cylinder 101 has at leastone air port (not shown) that allows air to be pumped into or out of thechamber. As shown in FIG. 2, the piston 102 is in its rightmost position(i.e., in a position furthest away from the valve nose 106). The piston102 has an O-ring groove 108 for holding a dynamic O-ring which acts asan air seal between chambers of the air cylinder 101. When air isselectively pumped into the chambers 104 such that the air pressure inthe rightmost chamber sufficiently exceeds the air pressure in theleftmost chamber, the piston 102 travels leftward towards the valve nose106. This leftward motion of the piston 102 pushes the valve rod 88leftward and expands the bellows 82. When the piston 102 extends thevalve rods 88 leftward, the seat/rod seal 94 compresses into the taperedbore of the valve seat 110, thereby closing off the flow of fluids inthe dispense head 49. The rod seal ring 90 is held in place within acavity of the dispense head 49 and has an O-ring groove 112 for holdinga static O-ring. The static O-ring acts as a fluid seal to prevent fluidin the dispense head 49 from leaking around the rod seal ring 90. Theresulting closed position configuration is shown in FIG. 3. Instead of apneumatic actuator such as the air cylinder, the system may utilize anelectronic actuator such as a solenoid to move the valve rods 88. Thesystem may also use any other actuator well known in the art.

The bellows assembly 80 in FIG. 3 is in the closed position becausethere is no gap between the seat/rod seal 94 and the valve seat 110,thereby preventing fluid from flowing into the exit passages 114 andinto the static mixer tube 50. A raised surface 116 on the piston 102prevents the piston surface from completely engaging the inner surfaceof the air cylinder 101 when the piston 102 is in its leftmost position.The raised surface 116 maintains at least some minimal air gap betweenpart of the piston surface and the air cylinder surface so that thepiston surface does not "stick" to the air cylinder surface.

To open the bellows assembly 80, the piston 102 is moved away from thevalve nose 106 so that the valve rod 88 moves relative to the rod sealring 90. This relative movement of the valve rod 88 to the rod seal ring90 compresses the bellows 82. The resulting configuration of the bellowsassembly 80 is the open position shown in FIG. 2 where the gap betweenthe seat/rod seal 94 and the valve seat 110 permits fluid to pass intothe exit passages 114. Hence, the fluid coming from the inlets 100 mayenter the dispense head 49 and flow out of the exit passages 114 of thedispense head 49. The opening and closing of the bellows assembly 80 actas a positive cutoff valve 70.

The valve seat 110 may be made of stainless steel or other suitablematerial. The seat/rod seal 94 may be formed of teflon or other suitablematerial that is deformable and yet highly impervious to chemicals. Thevalve body 118, valve nose 106, piston 102 and air cylinder 101 are madeof aluminum or other suitable material.

The dispense head 49 has no dynamic sealing surfaces. The primarysealing mechanism is the bellows assembly 80. A significant advantage ofsuch a dispense head is that none of the components which come incontact with the fluids being dispensed also come into contact with anymoving or dynamic sealing surfaces. Potential contamination may arisefrom moisture in the air which can cause the fluids to crystallize, orfrom contamination in the fluids themselves. Therefore, the dispensehead of FIG. 2 advantageously eliminates movement between any mechanicalcomponents of the dispense head 49 in the valve chamber and any fluidseal, thereby eliminating the possibility that a seal would be destroyedby the fluids or by abrasive contamination in the fluids.

FIG. 8 is a diagram of the pump stator assembly 130 of the progressivecavity pumps 34, 36. The pump stator assembly 130 is essentiallycomprised of multiple interlocking pressure sections 140 that have beeninserted into a metal hollow tube housing 132 with a locking end cap atboth ends. A threaded front end cap 142 receives the last pressuresection 140 at the front end of the stator assembly 130. A retainer 144attaches to tube housing 132 and the last pressure section 140 at therear end of the stator assembly 130. A threaded rear end cap 146 thenattaches to the tube housing 132.

FIGS. 9-12 illustrate different views of a pressure section 140 of thepump stator assembly 130. FIG. 9 is a side view of the pressure section140; FIG. 10 is a perspective end view of the pressure section 140; FIG.11 is an end view of the pressure section 140 of FIG. 10; FIG. 12 isanother side view of the pressure section 140; FIG. 13 is across-sectional view of the pump stator assembly of FIG. 8 andillustrates the resulting double helix flow pattern of fluids passingthrough the pump stator assembly.

Each pressure section 140 is made of teflon or other suitablydeformable, durable, yet highly chemically resistant and abrasionresistant material. Each pressure section 140 has a concentric 360degree double helix bore 141 running through its center. A first helixthread 138 and a second helix thread 139 of the bore are shown in FIG.13. The helix threads wind down the length of the bore 141, are opposedto each other by 180 degrees and cross each other every 180 degrees.Essentially, each pressure section 140 has one crossing of the doublehelix threads. To manufacture the double helix bore, a solid teflon rodis provided, a circular bore is drilled through the rod, and two helixthreads are carved out of the bore of the rod.

Each pressure section 140 has pins 148 which mate with holes 150 of anadjacent pressure section 140 to interlock the pressure sectionstogether and to maintain the radial alignment between adjacent pressuresections. The pressure section 140 has an O-ring groove 152. An O-ring(not shown) made of teflon or other suitably deformable yet durablematerial fits into the O-ring groove 152 between adjacent pressuresections to seal each pressure section. When the end caps 142, 146 aretightened to compress the pressure sections 140 together, the O-ringsexpand outward against the walls of the metal tube housing 132.

A rotor or screw 134 having a single helix thread is inserted throughthe double helix bore 141 of the interlocked pressure sections 140. Theinteraction of the single helix rotor 134 and the double helix bore 141creates the pumping action. FIGS. 14-16 illustrate how the single helixrotor operates within the double helix bore of a pump stator assembly.FIG. 14 is a cutaway view of a partial pump stator assembly having asingle helix rotor within the double helix bore.

Referring to FIG. 14, the single helix thread of the rotor 134 engagesportions of the double helix threads 138, 139 to create sealing lines136. Fluid may be carried between a pair of sealing lines 136. As therotor 134 turns within the double helix bore 141, the sealing lines 136move down the length of the bore, thereby transporting the fluid andcreating a progressive cavity pump. The desired total number of turns inthe double helix threads of the bore of the stator pump assembly 130depends on the desired pump characteristics.

FIG. 15 is a cross-sectional view of a rotor in a partial pump statorassembly (where the lines through the pump stator assembly do notrepresent the pressure sections but are used to correlate FIG. 15 toFIG. 16). FIG. 15 illustrates the sealing lines 136 formed by thecontacts between the rotor 134 and the double helix threads of the bore141 as well as the cavity 137 formed between adjacent sealing lines.FIG. 16 is a diagram showing the position of the single helix rotor asthe rotor rotates within the double helix bore of a pump statorassembly.

The bore 141 of the pressure sections 140 has an interference fit withthe rotor 134. That is, although the maximum outer dimension of therotor 134 exceeds the minimum inner dimension of the bore 141 of thepressure sections 140, the flexibility of the pressure sections 140permits the rotor to fit within the bore 141. The interference fitcreates a seal between the rotor 134 and the bore 141 by eliminating thegap between the rotor and the bore. Lack of a gap means that fluids areprevented from leaking back through the bore 141 of the pump. When fluidleaks back through the bore 141, the pump operates inefficiently andinaccurately. The interference fit also results in minimized slippage ofthe rotor 134 relative to the bore 141. Thus, the interference fitresults in a positive displacement pump wherein every rotation of thepump outputs an accurate and known volume of fluid. Because the pump isa constant displacement pump, the pressure of the system rises or fallsto a steady state depending on the viscosity and flow rate of thematerial being pumped, and the dynamic back pressure of the systemthrough which the fluid is dispensed. As this pressure is different foreach output requirement, it is imperative that the pressure bemaintained between cycles to insure accurate shot-to-shot dispensereproducibility.

By contrast, as pressures change unexpectedly in prior art devices, thefluid is compressed differently which results in a non-constant amountof fluid being dispensed. This problem with non-constant pressures isprevalent in prior art systems because as the dispense rate changes, thepressure changes. For example, a rotor that moves within a smooth boremay suffer from leakage and pressure changes. In such a pump, if fluidis poured into the bore having the rotor, the fluid will flow down thethread of the rotor, down the bore and out of the pump. The sealinglines of the double helix pump help prevent fluid from "pouring" throughthe pump.

Notably, each pressure section 140 can maintain a constant pressure evenwhen the rotor 134 is static. When the rotor 134 rotates, the fluidbeing dispensed is transported through the pump stator assembly 130 fromone pressure section to the next. The resulting progressive cavity pumpis able to maintain high pressure, is volumetrically accurate and has apulseless output flow. The pump is able to maintain constant volume ofthe fluids being dispensed, thereby insuring the accuracy of thedispensing characteristics. The flexible nature of the interlockedpressure sections and the metal hollow tube housing 132 of the pump alsohelp limit the tendency of the rotor 134 to nutate or twist duringrotation of the rotor 134.

FIG. 17 is an electrical block diagram of a preferred embodiment of themotor controller 180 of the present invention. The motor controller 180may be used to drive any motor described herein. The motor 182 is apermanent magnet DC brush or brushless motor and in particular, a 48volt 1/2 horsepower motor. The motor 182 is mechanically connected to anencoder 186. The encoder detects the absolute position of the motorshaft and sends this position information 188 to the control circuit190. The control circuit 190 can use the position information todetermine the rotational speed or acceleration of the motor. The controlcircuit 190 sends various control signals 192 and "ready" controlsignals 194 to a multiplexor 196. The ready signals 194 allow thecontrol circuit 190 to turn off any specific power driver 200 if thepower driver suffers a non-catastrophic failure. Signals from themultiplexor 196 pass to various power drivers 200. A DC-to-DC converter212 converts a 48 volt power supply to 5 volts which runs variouselectronics in the system and also sends 48 volts to the power drivers200. The power drivers 200 are semiconductor devices that use low levelinputs (i.e., signals from the multiplexor 196) to control relativelyhigh current level outputs (i.e., lines 220, 222) to control the motor182.

Three of the input signals are the brake control signal 202, directioncontrol signal 204 and the pulse width modulation (PWM) control signal206. The brake control signal 202 causes the power drivers 200 to shortthe lines 220, 222 going to the motor 182 which uses back electromotiveforce (emf) to dynamically brake or stop the motor 182 as quickly aspossible. The direction control signal 204 tells the power drivers 200whether to reverse the direction of the motor 182. The pulse widthmodulation control signal 206 carries a train of pulses and the powerdrivers 200 count the number of pulses over time. As the number ofpulses per unit time increases, the power drivers 200 outputincreasingly higher voltages up to a maximum of 48 volts to speed up themotor 182 accordingly. As the number of pulses per unit time falls, thepower drivers 200 reduce the output voltage to slow down the motor 182.

The power drivers 200 have current feedback lines 224 that returncurrent flow information to the control circuit 190. The control circuit190 uses the current flow information to see how hard the motor 182 mustwork to maintain a given speed. This information can be used to derivethe torque.

The control circuit 190 may receive information, analog or digital, fromdevices connected to the monitor port 228. For example, a temperaturesensor may be connected to the monitor port 228 to provide temperaturedata to the control circuit 190. A RS232 control port 230 facilitatescommunication between the control circuit 190 and the master controlunit 14 for motor information and commands. The RS232 control port 230allows the system to monitor the motor controller 180 for suchinformation as the desired motor speed, actual motor speed, desirednumber of total motor revolutions, actual number of total motorrevolutions, and current flow to each of the power drivers 200. A DIPswitch 232 may optionally be used to manually set the speed of theagitators which would otherwise be adjustable by the control circuit190. The DIP switch settings are sent over lines 234 to the controlcircuit 190.

Thus, the dispense system has various communication abilities. Thedispense system may be attached to an outside telephone line, allowingservice personnel at a remote location to monitor the system'sperformance and diagnose any malfunctions. A bar code reader may beattached to the dispense system where the system uses the bar codereader to identify a part, automatically configures itself to dispenseaccording to a known program, and displays an image of the part so theuser can verify that the program is the correct program for thedisplayed part. The system also may monitor material utilization, storein memory the total material used, and communicate with a manufacturingnetwork to provide material use information to an external computersystem.

FIG. 18 is a block diagram of a preferred embodiment of a dispensingsystem of the present invention which meters, mixes and dispensespowders and single or plural component fluids. The dispensing system iscapable of dispensing a powder and combining it with a single or pluralcomponent liquid, such as epoxy, silicone, urethanes, or adhesives. InFIG. 18, the dispensing system 275 has many of the same or similarcomponents as the dispensing system of FIG. 1. Components that remainthe same are identified by the same reference numeral.

The dispensing system 275 has a powder hopper 278 which holds thepowder. The powder hopper 278 has powder agitator bars 280 attached to amotor-driven auger 281. As certain powders may not flow over themselveseasily, resulting in air pockets, the agitator bars 280 mix the powderto eliminate air pockets. The auger motor 284 drives the auger 281 andis controlled by a motor controller 286. The master control unit 14sends control signals 287 to the motor controller 286. The auger motor284 has an encoder 288 for feeding motor information back to the motorcontroller 286. The master control unit 14 can use the motor informationto more accurately control the auger motor 284. For example, the augermotor 284 runs at a constant desired speed. However, as the level of thepowder in the powder hopper 278 falls, the current flow required todrive the auger motor 282 at the constant speed decreases. The mastercontrol unit 14 can measure the current flow to the auger motor 284 todetermine the level of powder remaining in the powder hopper 278.

Alternately, the system can be made to maintain a constant currentinstead of constant revolutions per second. In this alternate design, asthe powder level falls and as the current flow to the auger motor iskept constant, the rotational speed of the auger motor increases. Themaster control unit 14 can decrease the current to the auger motor whenthe master control unit 14 detects that the auger speed has increased.The master control unit 14 can also measure the rotational speed of theauger motor 284 to determine the level of powder remaining in the powderhopper 278.

The powder from the powder hopper 278 is dispensed into a centrifugalmixer 282. The singular or plural component liquid is also dispensedinto the centrifugal mixer 282. The output of the powder hopper 278injects the powder into the middle of the liquid. The centrifugal mixer282 has a stirrer 283 which stirs the powder into the mixture andprevents clumping. The stirrer 283 spins the mixture outwardly where itcan be dispensed out of the dispenser output 298. The centrifugal mixer282 blends the powder and liquid together into a homogenous materialwhich can then be dispensed in various shot sizes or at continuous flowrates. Thixotropic additives can be used to prevent settling of thesolids and to help keep the solids suspended in the liquid. Otheradditives can be included to accelerate the cure time so that lesssettling of the solids will occur.

The centrifugal mixer 282 is driven by a mixer motor 292 coupled to agear box 290. The gear box 290 permits the motor 292 to run at themotor's optimal speed while also allowing the centrifugal mixer 282 torun at the mixer's optimal speed which may differ from the motor'soptimal speed. Each of the motors in the dispensing systems of FIG. 1and FIG. 18 has a gear box which for simplicity purposes have only beenshown for the centrifugal mixer motor 292. The mixer motor 292 iscontrolled by a motor controller 294. The master control unit 14 sendssignals 295 to control the motor controller 294. An encoder 296 providesfeedback information about the mixer motor 292 to the motor controller294. The motor controller 294 can use the motor information to moreaccurately control the mixer motor 292.

Thus, the dispensing systems described herein have various types offeedback components. For example, the feedback components may includemotor controllers, pressure transducers, flow meters, current detectorsand any other components that obtain information about a device (such asa pump, motor, agitator, fluid line) and use (or let a control deviceuse) the information to control the device. The feedback componentsallow the dispensing system to dispense, meter and mix more accurately.

While the pumps 34, 36 output the same volume of fluid per pumprevolution, regardless of the density of the fluid, the dispensingsystem may require calibration prior to production runs. Prior artdispensing systems required the user to experiment by altering thevelocity or time duration of the pump.

The dispensing system of the present invention employs a calibrationprocess which separately calibrates each channel (channel A, channel B,channel C, etc.) of the system. Prior to the calibration run, the userreplaces the static mixer tube 50 with a calibration nozzle (not shown).The calibration nozzle does not mix the fluids from the two channelsinto one output nozzle, but instead has multiple output nozzles, one foreach channel. The user then weighs a first container on the scale 54 andzeroes the scale. The first container is placed under one of the outputnozzles. The user presses a foot pedal to begin the dispense cycle. Themaster control unit 14 instructs the pump 34, 36 of each channel tooutput a certain volume of fluid. Actually, the pumps dispense at a rateequal to 35% of the maximum rated motor speed so as to better "weight"the accuracy of small shot sizes. The fluid from channel A is dispensedinto the first container. The user weighs the first container on thescale 54 and inputs the weight in grams into the keypad. Based upon thenumber of revolutions made by the pump and the weight of fluiddispensed, the master control unit 14 can compare the expected weight ofthe fluid dispensed with the actual weight dispensed. The master controlunit 14 computes a number that represents the number of encoder ticksper gram for channel A. This calibration process is independent of thepump type, gear ratio, encoder resolution, motor horsepower and thelike. All of these variables are taken into account in the singlecomputed number. The process is repeated with a second container forchannel B.

Advantageously, the effects of temperature, varying pressure, transientimbalance phenomena and other variables on the actual volume of fluiddispensed are eliminated. Such a system also permits the user todispense accurately by weight or by volume. Additionally, the systemscan be calibrated for differing fluids, dispense amounts, flow rates,ratios and the like. This calibration system is quick and easy toexecute.

The dispensing system is easily programmable by a user to control orchange the flow rate, ratio, quantity and/or other dispensing criteriain any manner. FIG. 19 illustrates how the software flowcharts shown inFIGS. 20-23 fit together. The software flowchart of FIGS. 20-23 controlsthe overall aspects of the dispensing system. First, in block 300, thesystem initializes various hardware components such as communicationports, serial ports and other circuits. In block 302, the system loads amachine data file that contains information specific to the system suchas the pump types and ratios of the gear boxes. In block 304, the systemchecks to see if the user enabled the pressure relief switch (i.e., anemergency stop switch). If enabled, the system will shut down thesystem, interrupt any dispense cycle, stop the pump motors 34, 36 andopen the dispense head 49 (step 306) to relieve the overpressurecondition. Otherwise, the system checks the fluid levels in the vats 2,4 (step 308). If empty or low, an Empty flag is set (step 310). If notempty, the system reads the pressure in the pump fluid lines 46, 48 asprovided by the pressure transducers 58, 60 (step 312). If the detectedpressure exceeds a preset pressure limit, the system finds overpressure(step 314), stops the pump motors, and lights LEDs to warn the user(step 316). When the pressure is within normal operating conditions, theuser can dispense in either a timed dispense mode or a continuous runmode. The system checks if the user entered a time duration for thedispense cycle (timed dispense mode) in step 318. If YES, the systemwaits for the user to depress the foot pedal (step 320) and in response,the system starts the dispense cycle and the system retrieves thedesired time, calculates the stop time, opens the dispense head andstarts the pump motors (step 322). If the system was in a timed run modeand the time has expired (step 324), the system will stop the pumpmotors and close the dispense head (step 326).

If the user selected the continuous run mode instead of the timed run,the system waits for the user to depress the foot pedal (steps 328, 332)which causes the system to open the dispense head and start the pumpmotors (steps 330, 334). At step 336, the system checks to see if anyuser inputs were made on the LCD display panel. At any time other than adispense cycle, the user may enter the set parameters routine via thedata entry keyboard 20 or 22.

The user's depression of the Ratio key (step 338) allows the user toenter the desired ratios for each constituent fluid (step 340). If thedesired ratios do not total 100%, the system will require the user tore-input desired ratios (step 342). When correct ratios are entered, thesystem computes the new quantities of fluids desired and recalculatesthe correct pump speeds to use (step 344).

If the user depresses the Time key (step 346), the user may input thedesired run time (step 348). The system then computes the correct pumpspeeds for this desired run time (step 350).

If the user depresses the Quantity key (step 352), the user may inputthe desired total quantity of the end product in grams (step 354). Basedupon the desired weight of the end product, the system calculates newquantities and pump speeds (step 356).

If the user depresses the Calibrate key (step 358), the user can startthe calibration process. In the calibration process, the user places acontainer under the output nozzle of channel A (step 360). The userstarts the dispense cycle by depressing the foot pedal (step 362), whichcauses the dispense head to open and the pump motors to start (step364). At step 366, the system checks to see if the dispense cycle iscompleted. If YES, the pump motors are stopped and the dispense headclosed (step 368). The user takes the container with the dispensed fluidfrom channel A, weighs it on the scale 54, and enters the weight ingrams on the keypad (step 370). The system takes the weight informationand computes the number of encoder ticks per gram (step 372).Alternately, the system could calculate the density of the fluid asgrams/cc. The calibrated number of ticks per gram for channel A is savedin the machine data file (step 374). This calibration procedure isrepeated for each fluid (step 376).

If the user depresses the Program key (step 378), the user may select aprogram (step 380) previously stored in the machine data file. Thisselected program which may contain the user's most commonly used ratiosor quantities is loaded into the system (step 382).

If the user wants to save a program into the machine data file, the userdepresses the Store key (step 384) and saves the program under anidentifying program number (step 386). This new program is stored by thesystem in the machine data file (step 388).

Turning to FIG. 24, the software flowchart for controlling the motorcontroller 180 over the RS232 port 230 and DIP switch 232 is shown. Aspreviously indicated, the motor controller can control the speed,direction and on/off of the motor. Starting at step 400, the systemchecks to see if information was received over the RS232 port or the DIPswitch. If the information came from the DIP switch, the DIP switchsettings are read (step 402). If information was received over the RS232port, the system retrieves the last buffered values for the speed,direction and desired number of encoder ticks for the motor controller.At step 406, the system compares the new values with the old values. Ifthe new values are different, the new values are saved and used by thepower drivers 200 to control the motor (step 408).

The software flowchart of FIG. 25 illustrates how the master controlunit 14 of the system controls and queries the motor controller 180. Themaster control unit 14 uses the RS232 port 230 either to set new valuesinto the motor controller or to query the motor controller for thesevalues. If the master control unit 14 wants to set new values into themotor controller, the master control unit sends a command to the motorcontroller that is not prefaced by the "?" character (step 420). Themaster control unit 14 can set the desired velocity of the motor (step422) with a "V" command (step 424), the encoder ticks (step 426) with an"E" command (step 428), or the direction of the motor (step 430) with a"D" command (step 432). The master control unit 14 can instruct themotor controller to start the motor (step 434) with a "GO" command (step436) or to stop the motor (step 438) with a "STOP" command (step 440).

If the master control unit 14 wants to query the motor controller forthe velocity of the motor (step 444), the master control unit 14 sends a"V" command prefaced by a "?" (step 446) which causes the motorcontroller to output the velocity information onto the RS232 line (step448). Similarly, the master control unit 14 can obtain the encoder ticksread (step 450) with an "E" command (step 452), the direction of themotor (step 454) with a "D" command (step 456), or the current flow tothe motor (step 458) with a "C" command (step 460). Erroneous commandsare indicated by steps 442 and 446.

The motor controller 180 uses a timer interrupt scheme to ensure thatthe motor is accurately controlled. FIG. 26 shows the software flowchartfor this timer interrupt. A timer is set to the timeout period (step480) which may be approximately 6 milliseconds. When this timer expires(step 482), the motor controller reads the number of encoder ticks readduring the 6 millisecond period (step 484) and updates the total numberof ticks read thus far with this number (step 486). The motor controllerthen compares the total number of ticks read against the desired numberof ticks to be read (step 488). If the numbers match, the motorcontroller directs that the motor should be braked and stopped (step490). If the numbers do not match yet, the motor controller compares thenumber of ticks read during the 6 milliseconds with the desired numberof ticks to be read during the 6 milliseconds and determines whether theactual motor speed is too slow or too fast (step 492). If the actualspeed is too slow or too fast, the motor controller adjusts the speed(step 494).

While the invention is susceptible to various modifications andalternative forms, specific examples thereof have been shown by way ofexample in the drawings and are herein described in detail. It should beunderstood, however, that is not intended to limit the invention to theparticular forms disclosed, but on the contrary, the invention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the followingclaims.

We claim:
 1. A dispense head for a plural pump dispensing system,comprising:a body including chambers, exit passages from the chambers,respectively, and inlets to the chambers, respectively; pumps coupledwith the inlets, for communication with the inlets, respectively;cylindrical bellows within the chambers, respectively, each including afirst end and a second end, the first end being sealed to the body;rods, each including a sealing end, the rods extending slidably into thechamber through the first end of the bellows and being sealed to thesecond end of the bellows; an actuator coupled to the rods, the actuatorhaving a first extreme position with the sealing ends of the rodsextending to the body at the exit passages to close the exit passagesand a second extreme position with the sealing ends of the rodsdisplaced from the body at the exit passages to open the exit passages;a controller coupled with the pumps and with the actuator, thecontroller selectively simultaneously stopping the pumps and driving theactuator to the first extreme position and selectively simultaneouslystarting the pumps and driving the actuator to the second extremeposition.
 2. The dispense head of claim 1, the actuator being apneumatic actuator.
 3. The dispense head of claim 2, the pneumaticactuator including an air cylinder with an air chamber, a port extendinginto the air chamber and capable of carrying air into and out of the airchamber and a piston within the air chamber and coupled to the rod, thepiston moving within the air chamber when air is carried into the airchamber.
 4. The dispense head of claim 3 further comprising:an O-ringmounted to the piston and acting as an air seal.
 5. The dispense head ofclaim 3, the piston having a raised surface integrally formed thereon.6. The dispense head of claim 1 wherein the movement of the rods toclose the chambers expands the bellows.
 7. The dispense head of claim 1wherein the movement of the rods to open the chambers compresses thebellows.
 8. The dispense head of claim 1 further comprising:a staticmixer coupled with the exits.